1. Field of the Invention
This invention relates to transmissions having multiple load sharing countershafts, including means to assure that the torque transmitted by each countershaft is substantially equal, and, in particular, this invention relates to transmissions having multiple, substantially identical load sharing countershafts and utilizing herringbone (also called twin-helical) gearing.
2. Description of the Prior Art
The advantages of utilizing multiple, substantially identical, load sharing countershafts in heavy duty change gear transmissions are well known in the prior art and may be appreciated by reference to U.S. Pat. Nos. 3,105,395; 3,335,616; 3,500,695; 3,611,823 and 4,226,135, the disclosures of which are hereby incorporated by reference.
The advantages of heavy duty change gear transmissions utilizing helical gearing are also well known in the prior art as may be appreciated by reference to U.S. Pat. Nos. 3,772,934 and 3,885,446, the disclosures of which are hereby incorporated by reference.
The advantage of herringbone or double-helical gearing over single-helical gearing, namely, the fact that the axial thrust forces associated with single helical gearing are balanced within the double-helical gear itself resulting in a net axial force of substantially zero, is also well known in the prior art. Herringbone gearing utilized in change gear transmissions may be seen by reference to U.S. Pat. Nos. 3,600,962; 4,429,586 and 4,361,058, the disclosures of which are hereby incorporated by reference.
While the prior art transmissions having multiple, substantially identical, load sharing countershafts, especially the twin countershaft type having a floating mainshaft/floating mainshaft gear structure for radial self-alignment of the gears into an equal or substantially equal load sharing position, have been extremely commercially successful, there does not now exist a commercially available change gear transmission having herringbone or double-helical gearing and multiple load sharing countershafts with means to assure that the load transmitting gearing will tend to automatically self-align into a position wherein each of countershafts transmits a substantially equal torque load.